To carry out folding a folded box of a given material, it is known to convert a blank of said material in a machine called a <<folder-gluer>>.
A blank is usually composed of two large faces, a first face called an internal face, intended to shape the inside of the folded box and a second face called an external face, intended to shape the outside of the box.
With regard to the running direction of the blanks in the folder-gluer, the front edge of the blank is the transverse side of the blank which first enters into the machine and the rear side is the one which last enters. Likewise, the left edge of the blank is the lateral side of the blank located at the left side of the longitudinal axis of the folder-gluer and the right edge is the lateral side of the blank located at the right side of the longitudinal axis of the folder-gluer.
In a folder-gluer machine, the folding operation of a blank is achieved during its conveying through the folder-gluer, using folding tools working together on each side of the blank. The tool located on the side of the internal face of the blank is called an internal tool and the tool located on the side of the external face of the blank is called an external tool.
At the end of a folding operation, the blank is divided into three longitudinal adjacent parts: a first panel, a fold and a second panel folded down onto the first panel. For convenience, this terminology will be used for a blank, i.e. before the folding operation. The first panel is linked to the second panel by the fold defined by an axis and a radius. The axis and the radius of the fold are respectively called its folding axis and its folding radius.
Usually, a conveyor conveys the blank along a substantially planar path from the inlet towards the outlet of the folder-gluer. During the folding operation, the internal tool is pressing against the internal face of the blank along the longitudinal fold and the external tool is pressing against the external face of the first panel. During the conveying of the blank, the external tool exerts onto the first panel a bending force which is applied on the front edge of the panel for causing the rotation of the first panel around the folding axis. In this known folding process, the position and the geometry of the fold are difficult to control, particularly when folding between 0 and 90°, which causes variations in the production of the folded boxes and thus quality problems. These problems are particularly acute when the panel to be folded is stiff, as is notably the case when the blank is a corrugated board blank.